1. Field of the Invention
The present invention relates generally to an expression regulatory element which is operable in plants. More particularly, the present invention provides an expression regulatory element in the form of a promoter operable selectively in endosperm tissue of oil palm plants. Even more particularly, the present invention is directed to the promoter associated with a gene encoding glutelin in endosperm tissue of oil palm plants. The present invention also contemplates other expression regulatory elements, such as enhancers and/or silencers, which are associated with the glutelin gene promoter or are positioned proximal thereto or which otherwise modulate the activity or function of the glutelin gene promoter. The expression regulatory elements of the present invention have utility, inter alia, in the facilitation of tissue specific expression of desired nucleic acid molecules in operable connection thereto which encode, inter alia, RNA which is optionally translated to a peptide, polypeptide or protein. In at least oil palm plants. The expression is tissue specific for the endosperm. Furthermore, the present invention additionally provides a novel isolated glutelin protein and the genetic sequences encoding same.
2. Description of the Prior Art
Bibliographic details of the publications referred to in this specification are also collected at the end of the description.
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.
Two different types of storage oil are obtained from oil palm fruits, palm oil from the mesocarp and kernel oil from the kernel. Both oils are different in fatty acid composition, physical properties and usability. Kernel oil is synthesized in the endosperm between 11 and 14 weeks after anthesis (waa). It is rich in medium chain saturated fatty acid namely, 50% lauric acid (C12:0) and 15% myristic acid (C14:0), which serve as important feedstocks for the oleochemical industry. It also contains 15% linoleic acid (C18:2) and lower levels of palmitic acid (C16:0), capric acid (C10:0) and caprylic acid (C8:0), contributing about 7%, 4% and 4%, respectively. Palm kernel meal, the by-product from oil extraction is a valuable animal feed. Oil synthesis in the mesocarp starts later at around 15 waa and stops when the fruits ripen at 20 waa. Palm oil contains 44% palmitic acid (16:0), 5% stearic acid (18:0), 39% oleic acid (18:1) and 10% linoleic acid (18:2). The main applications of palm oil products are in the edible field, however non-food uses such as in cosmetics and as biofuel are advancing.
Being storage tissues, oil palm mesocarp and kernel can be the target for accumulating genetically engineered products without deleterious effects on the plants. It would be highly desirable to manipulate the biochemical pathways for designer oil synthesis in the kernel without affecting mesocarp oil production. The amino acid composition of kernel proteins may also be altered to increase their nutritional values. The kernel would also be suitable target for accumulating high value nutraceuticals and pharmaceuticals by genetic manipulation. To achieve these goals, it is essential to isolate kernel-specific gene promoters and to have an understanding on the regulation of gene expression in the kernel.
Seed storage proteins are synthesized at high levels in the cotyledon and embryo of dicotyledonous plants or in the endosperm of monocotyledonous plants and deposited in protein bodies in the cells of these tissues. The expression of these genes is tightly regulated, thus providing a valuable system for studying molecular mechanisms controlling seed-specific gene expression in higher plants. Seed storage gene promoters have been successfully used for controlling expression of introduced genes to modify oil composition in transgenic oil seed crops. These include utilization of the napin gene promoter for rapeseed (Voelker et al., Science 257: 72-73, 1992) and β-conglicinin gene promoter for soybean Kinney, Journal of Food Lipids 3: 273-292, 1996). There is also great interest to use promoters from seed storage protein genes to target production of high value novel products to the seeds. The endosperm-specific glutelin gene promoter from rice for example is being used to produce transgenic rice lines with increase level of pro-vitamin A (GoldenRice) (Beyer et al., Proceedings of the American Society for Nutritional Sciences Symposium on Plant Breeding: 506S-510S, 2002) and for the production of subunit vaccine in the seeds of transgenic tobacco (Tackaberrry et al., Genome 46(3): 521-526, 2003).
Seed storage proteins are classified based on differences of their solubility properties. Saline-insoluble glutelins are found in rice, wheat and other cereals. Glutelins are the major seed storage proteins in rice accounting for more than 80% of the total protein content in the endosperm (Shewry, Biol. Rev. 70: 375426, 1995). Typically, seed storage proteins including, glutelin, are encoded by complex multigene families. Sequence analysis revealed that rice glutelins are more closely related to saline-soluble 11S globulins found largely in dicotyledonous species (Muntz, Plant Molecular Biology 38: 77-99, 1998). Rice glutelins are synthesized as precursor proteins, which encode an acidic and a basic protein subunit, plus a leader peptide for targeting to the endoplasmic recticulum. The two protein subunits separate post-translationally but subsequently reassociate via formation of disulphide linkages between their cysteine residues. Several polypeptides join together forming an oligomer with suitable conformation to be deposited into protein bodies (Takaiwa et al., Plant Mol. Biol. 17(4): 875-885, 1991).
In accordance with the present invention, a tissue-specific expression regulatory element, is identified for endosperm tissue of an oil palm plant, which enables tissue specific expression of nucleic acid molecules associated therewith.